[ci] Migrate test jobs to vmss agent pool to increase node limit. (#14127)

Why I did it
original ubuntu-20.04 agent pool has a node limit 35.
Use vmss agent pool to get higher node limit.

How I did it

Author: liushilongbuaa

azure-pipelines.yml

@@ -176,8 +176,7 @@ stages:
         section: part-2
 
   - job: t0_testbedv2
-    pool:
-      vmImage: 'ubuntu-20.04'
+    pool: ubuntu-20.04
     displayName: "kvmtest-t0 by TestbedV2"
     timeoutInMinutes: 240
     condition: and(succeeded(), eq(variables.BUILD_IMG_RUN_TESTBEDV2_TEST, 'YES'))
@@ -190,8 +189,7 @@ stages:
         MAX_WORKER: $(T0_INSTANCE_NUM)
 
   - job: t0_2vlans_testbedv2
-    pool:
-      vmImage: 'ubuntu-20.04'
+    pool: ubuntu-20.04
     displayName: "kvmtest-t0-2vlans by TestbedV2"
     timeoutInMinutes: 240
     condition: and(succeeded(), eq(variables.BUILD_IMG_RUN_TESTBEDV2_TEST, 'YES'))
@@ -254,8 +252,7 @@ stages:
         vmtype: ceos
 
   - job: t1_lag_testbedv2
-    pool:
-      vmImage: 'ubuntu-20.04'
+    pool: ubuntu-20.04
     displayName: "kvmtest-t1-lag by TestbedV2"
     timeoutInMinutes: 240
     condition: and(succeeded(), eq(variables.BUILD_IMG_RUN_TESTBEDV2_TEST, 'YES'))
@@ -321,8 +318,7 @@ stages:
 
   - job: multi_asic_testbedv2
     displayName: "kvmtest-multi-asic-t1-lag by TestbedV2"
-    pool:
-      vmImage: 'ubuntu-20.04'
+    pool: ubuntu-20.04
     timeoutInMinutes: 240
     condition: and(succeeded(), eq(variables.BUILD_IMG_RUN_TESTBEDV2_TEST, 'YES'))
     continueOnError: false
@@ -336,8 +332,7 @@ stages:
           NUM_ASIC: 4
 
   - job: dualtor_testbedv2
-    pool:
-      vmImage: 'ubuntu-20.04'
+    pool: ubuntu-20.04
     displayName: "kvmtest-dualtor-t0 by TestbedV2"
     timeoutInMinutes: 240
     condition: and(succeeded(), eq(variables.BUILD_IMG_RUN_TESTBEDV2_TEST, 'YES'))
@@ -352,8 +347,7 @@ stages:
 
   - job: sonic_t0_testbedv2
     displayName: "kvmtest-t0-sonic by TestbedV2"
-    pool:
-      vmImage: 'ubuntu-20.04'
+    pool: ubuntu-20.04
     timeoutInMinutes: 240
     condition: and(succeeded(), eq(variables.BUILD_IMG_RUN_TESTBEDV2_TEST, 'YES'))
     continueOnError: false
@@ -370,8 +364,7 @@ stages:
 
   - job: wan_testbedv2
     displayName: "kvmtest-wan by TestbedV2"
-    pool:
-      vmImage: 'ubuntu-20.04'
+    pool: ubuntu-20.04
     timeoutInMinutes: 240
     condition: and(succeeded(), eq(variables.BUILD_IMG_RUN_TESTBEDV2_TEST, 'YES'))
     continueOnError: false